A prodigiously gifted singer and improviser who'd left his native Ghent to hit the roads of Europe, Agricola was coveted by the courts of France and Burgundy as well as the Medici and d'Este families. In his early 50s when he died, he left a large body of work, including his magnum opus, a mass called In myne zyn.

If this sounds like an odd title for a mass in Latin, that's because it is borrowed from a three-part love song that was on everybody's lips at the time. In myne zyn is an old spelling of in mijn zin, or "in my mind".

Agricola turned it into an obsessive leitmotif, passing it from one voice to the next, changing its rhythm or drowning it under a sea of ornaments. Other songs were also blended in, some of them pious, others secular or even racy.

For a composer today to weave snatches of Jacques Brel's "Ne me quitte pas", Schubert's Ave Maria and the Rolling Stones' "Let's Spend the Night Together" into a coherent and solemn whole would be pretty unthinkable, but this mixture of religious and secular was much more common back then. "Physical love was seen as the most sacred thing, as it could create new life," explains Dirk Snellings, the bass singer and artistic director of the Leuven-based vocal quartet Capilla Flamenca, who've just recorded a CD of the mass and will be performing it live next month.

The musicologist who wrote the CD's liner notes likens the piece to the teeming world of Flemish primitive Jan Bruegel, where various scenes are played out side by side, mixing high and low, comic and tragic, and peppered with allusions and jokes that are often lost on us today.

"There is so much happening in it at the same time," agrees Snellings (pictured in the very middle of the photo). "For the listener, it feels as mysterious as standing in front of a piece of Arabic calligraphy, staring at all those different lines that somehow fit together. You can choose to focus on this voice, or follow that ornament. It's simply spellbinding."

Named after the group of singers that Charles V took along with him when he left his native Ghent in 1517 to become king of Spain, Capilla Flamenca are among today's most bewitching ambas- sadors of the so-called Franco-Flemish school, the intricate polyphony that flourished in the Low Countries in the 15th and 16th centuries and spread all over Europe. Made up of four male Flemish singers, the group radiates mutual empathy - the kind that comes with years of working together.

Capilla Flamenca have revived exquisite motets, courtly love songs and rousing Christmas music by the likes of Roland de Lassus and Pierre de la Rue. But In myne zyn is probably their most daunting project so far.

"Even by the standards of the time, this was highly complex music," Snellings says. "It was Agricola's last mass, and you can't help feeling he wanted to pour everything he could do into it."

Agricola, it turns out, was largely untouched by the Renaissance ideal of structure and clarity that was beginning to sweep over Europe. His feet still firmly planted in the Middle Ages, his aim was to overwhelm, if only to give his listeners a sense of the afterlife and a glimpse at the complexity of the cosmos.

Today, this music can be enjoyed by just sitting back and letting yourself be swept away by this great ocean of sound - my five-year-old daughter has started to play it when she needs to unwind after a busy day. But it also helps if you know what to listen out for, which is why the CD includes recordings of the original songs, effectively providing us with some of the musical culture that Agricola's contemporaries would have shared. It is then enormously satisfying to follow the melody as it weaves in and out of the mass, morphing from simple ditty to ever-more-sophisticated polyphony.

Capilla Flamenca also has made a video of the piece, which will soon be posted on their website. It is probably the first of its kind in the early music world, although the underlying concept is hardly new: "People would look at paintings as they stood listening in the church," says Snellings, who also regularly sings in art exhibitions and will perform at the inauguration of Ghent's new STAM museum next month. "The pictures made clear what the words and music didn't - they were the Bible of the poor."

Capilla Flamenca does its best to reach out to modern audiences. In 2003, they took part in Foi, an arresting contemporary dance production by Sidi Larbi Cherkaoui, their suave voices providing a striking counterpoint to the apocalyptical world depicted on stage.

"We live in the present," says Snellings. "Look at Leuven, it still has lots of beautiful old buildings, but there are some fine modern ones as well." Still, he and his friends are never happier than when performing in the churches for which this music was composed, such as the Abbey van 't Park in Heverlee where the CD was recorded. "Our voices rise and fill the space, developing rich harmonics. We can make the sound light, brilliant or soft. It all feels natural and effortless."

In myne zyn
2 October, 20.00
Sint-Niklaas van Tolentijn Church Kerkplein, De Pinte
www.capilla.be